Kurzweil 900 MX Pt. 2

Well, it was a bit of a battle, but I finally have a working display for the Kurzweil!

The removal and replacement of the LCD itself wasn’t too difficult, but the backlight didn’t appear to be working on the new LCD. So I checked the two connection pins on the circuitboard, but couldn’t detect any power coming out of them.

I then checked the specs for the LCD and which revealed it accepts a maximum of 13V, so I hooked up a 9v battery to it and the backlight burst into life.

I guess there’s a component somewhere in the circuit which has failed or a dry solder point perhaps, but a quick visual inspection didn’t reveal anything obvious, so I decided to look for an alternative 9v source.

Fortunately, the 900 MX has an external 9v wall wart PSU, so I ran wires from the input socket and power switch to the backlight. The reason for running it after the power switch of course is because otherwise the backlight would be permanently on!

After reassembly, I did some testing and found that there was good and bad news.

The good news

I could navigate through the menus fine, select patches and change MIDI settings. All buttons work too.

The MIDI indicator responds to incoming data from my controller. In fact, the MX has a handy built in MIDI monitor function so I could see the note on / off information as well as pitch bend.

The bad news

It doesn’t make any sound. Pretty bad news I think you’ll agree.

So I whipped the top off again to have a good stare at the circuit board. I noticed two IC’s with Left and Right screen-printed below them on the circuit board, so guessed that might be a good place to start. The IC’s were marked PCM56P, which I think are Digital to Analog converters (DAC’s).

However, the likelihood of both DAC’s failing at the same time seemed unlikely, so I carried on looking for any shared components in the same general area. That’s when I chanced upon a relay by American Relays Inc, marked AD2A05D. I must profess, I didn’t really know what it did, but it was positioned on the circuit board between the DAC’s and the output phono jacks so I guessed the sound must be somehow routed through it.

I then chanced upon a webpage dedicated to problem solving for the Kurzweil K1000 http://k1000.net/problems.htm which revealed I could be onto something. Under the heading ‘No Sound or Distorted Sound’ it read..

“This is most often caused by a faulty audio output relay – a relay that connects the audio to the two output jacks on the back of the expander or keyboard. If the relay gets stuck or fails, no sound will be heard at the output jacks.”

So I’m hoping that’s also what’s wrong with my MX. Being in the UK, the chances of finding the original relay are nil, but I managed to find what I think is a compatible one on ebay. It’s the Hamlin HE722A0510 which is a 5v DPST reed relay with diode.

To be continued…